Xenopus Polycomblike 2 (XPcl2) controls anterior to posterior patterning of the neural tissue

A novel gene, Xenopus Polycomblike 2 (XPcl2), which encodes a protein simil ar to Drosophila Polycomblike was cloned and characterized. Polycomblike be longs to the Polycomb group proteins, which maintain stable expression patt erns for the clustered homeotic genes in the Drosophila embryo by forming m ultimeric complexes on chromatin. XPcl2 shows greater amino acid sequence h omology to human and mouse M96 (hPcl2, mPcl2) than Xenopus Pcl1 (XPcl1), mo use Tctex3 (mPcl1) and human PHF1 (hPcl1), indicating that at least two typ es of Polycomblike genes are conserved between amphibians and mammals. XPcl 2 mRNA is present both maternally and zygotically, and the temporal express ion profile is distinct from XPcl1, another member of the Polycomblike fami ly in Xenopus. XPcl2 is highly expressed in the anterior-dorsal region of X enopus following the neurula stage in a manner similar to XPcl1. Overexpres sion of XPcl2 disturbs the develop ment of the anterior central nervous sys tem, eye and cement gland. In the XPcl2-overexpressing embryo, a hindbrain marker, Krox20, and a spinal cord marker, HoxB9, are expressed more posteri orly, suggesting an alteration in the anterior-posterior patterning of the neural tissue. In addition, XPcl2 represses Zic3- and noggin-induced anteri or neural markers, but not neural crest markers in animal cap explants. The se results indicate that XPcl2 regulates anterior neural tissue development and the anterior-posterior patterning of the neural tissue.